A relatively recent convenience feature available to many wireless communications devices is the use of a short range communications network, such as a Bluetooth network, to enable the use of a wireless headset when conversing on the wireless communications device. The wireless headset permits the user to communicate without the use of hands, freeing the user's hands to perform other tasks, such as driving, writing, typing, and so forth. Another added advantage of the wireless headset is the convenience afforded with the elimination of the wire that would otherwise be connecting the wireless headset to the wireless communications device.
Wireless communications devices continue to decrease in size while accumulating more features and functions. Today, it not uncommon to find wireless communications devices that maybe significantly smaller than a deck of playing cards boasting multi-band functionality, as well as extraneous features such as data management, short range wireless data communications, image and video capture, and multimedia capability, to name a few. Often included in the multimedia functionality includes the ability to receive FM transmissions and play the FM transmissions through speakers of the wireless communications device or a set of wired headphones connected to the wireless communications device.
FIG. 1a illustrates a frequency spectrum of the FM band. The FM band starts at about 87.9 MHz and ends at about 107.9 MHz. In order to adequately receive an FM signal, an antenna of appropriate length may be needed. The wavelength of a 87.9 MHz signal is about 3.41 meters (M), while it is about 2.78 M for a 107.9 MHz signal. Clearly, an antenna greater than 2.78 M in length is not feasible for use in a wireless communications device. Good performance may be achieved when antennae of fractional wavelengths are used. Antennae with lengths of about ½, ¼, or ⅛ the wavelength of the signals being received may yield sufficient performance. FIG. 1b illustrates a table of ½, ¼, and ⅛ wavelengths for FM signals at about 87.9 MHz and 107.9 MHz as well as for an exemplary 2.4 GHz signal.
Even a ⅛ wavelength antenna, about 0.35 M in length, may be impractical for inclusion in a wireless communications device. An antenna of such a great length may not be embedded inside the wireless communications device and may have to be externally attached to the wireless communications device. However, attaching such a long antenna to a wireless communications device may increase its bulk and reduce the practicality of the wireless communications device, potentially negating some of the advantages of the wireless communications device.
FIG. 2 illustrates a prior art system 200 for adding an external antenna of sufficient size to provide adequate FM reception performance. The system 200 includes a wired headset 205 coupled to a wireless communications device 210, wherein a wire 215 connecting the wired headset 205 to the wireless communications device 210 may be used as an antenna. Since the wire 215 should be on the order of several feet to several meters in length to enable a practical wired connection between the wired headset 205 and the wireless communications device 210, the wire 215 may function well as an antenna. The user may control the operation of the wireless communication device 210 operating as an FM receiver with a built-in user interface of the wireless communications device 210.
The wireless communications device 210 includes a radio frequency (RF) integrated circuit 220 that may include an FM tuner 225 and a Bluetooth unit 230. A Bluetooth wireless headset 235 may enable a user to operate the wireless communications device 210 wirelessly. An antenna 240 may enable the wireless communications device 210 to communicate with the Bluetooth wireless headset 235 and to various cellular communications networks. The antenna 240 may be an external or an internal antenna. Since the operating frequency of a Bluetooth communications network is about 2.4 GHz, a full wavelength is only 0.125 M. Therefore, a quarter-wavelength antenna is only 0.016 M in length, which may make the antenna easier to embed in a small form-factor wireless communications device.